HKUDS/Vibe-Trading · error · TypeError

{model}: generated_at must be a datetime.datetime supplied b

Error message

{model}: generated_at must be a datetime.datetime supplied by the caller, got {type(value).__name__}. This module never calls datetime.now() -- pass datetime.now(timezone.utc) yourself.

What it means

_require_generated_at enforces that generated_at is a datetime.datetime explicitly supplied by the caller. The module deliberately never calls datetime.now() itself, so artifact timestamps are deterministic and reproducible; a non-datetime (string, date, float) is a TypeError.

Source

Thrown at agent/src/quantlib/valuation/artifact.py:352

def _require_generated_at(value: datetime, model: str) -> datetime:
    """Check that a caller-supplied timestamp is usable, and only that.

    This function never reads a clock. Its only job is to reject a call that
    did not supply one properly -- see the module docstring.

    Args:
        value: The candidate ``generated_at``.
        model: Name of the calling builder, for the error message.

    Returns:
        ``value`` unchanged.

    Raises:
        TypeError: If ``value`` is not a ``datetime.datetime``.
        ValueError: If ``value`` is timezone-naive.
    """
    if not isinstance(value, datetime):
        raise TypeError(
            f"{model}: generated_at must be a datetime.datetime supplied by the "
            f"caller, got {type(value).__name__}. This module never calls "
            "datetime.now() -- pass datetime.now(timezone.utc) yourself."
        )
    if value.tzinfo is None or value.utcoffset() is None:
        raise ValueError(
            f"{model}: generated_at must be timezone-aware (e.g. "
            "datetime.now(timezone.utc)), got a naive datetime "
            f"{value!r} -- an artifact's timestamp must be unambiguous."
        )
    return value


# ---------------------------------------------------------------------------
# Canonical normalization: numbers, then the recursive flatten/hash engine
# ---------------------------------------------------------------------------

View on GitHub (pinned to 80ffdda44c)

Solutions

Pass datetime.now(timezone.utc) (or a fixed aware datetime for reproducibility).
When parsing from text, use datetime.fromisoformat(value) and ensure tzinfo is set.
Use datetime.datetime, not datetime.date.

Example fix

# before
build_dcf_artifact(generated_at="2026-01-01", ...)
# after
from datetime import datetime, timezone
build_dcf_artifact(generated_at=datetime.now(timezone.utc), ...)

Defensive patterns

Strategy: type-guard

Validate before calling

from datetime import datetime
if not isinstance(generated_at, datetime):
    raise TypeError("generated_at must be a datetime.datetime")

Type guard

from datetime import datetime
def is_datetime(value) -> bool:
    return isinstance(value, datetime)

Prevention

Use datetime.now(timezone.utc) at call sites; never strings.
When loading from JSON, parse timestamps with datetime.fromisoformat.

When it happens

Trigger: build_dcf_artifact(generated_at="2026-01-01", ...); passing a datetime.date instead of datetime.datetime; passing a Unix timestamp float or None.

Common situations: Loading timestamps from JSON/YAML as strings; refactoring code that used date objects; test fixtures written with plain dates.

Understand the failure class

Background: "Wrong argument type", "must be a string", "expected Array or Prism::Scope": TypeError and ArgumentError when a library receives a value of the wrong type — this error's family across 28 libraries.

Related errors

AI-assisted analysis of HKUDS/Vibe-Trading@80ffdda44c (2026-08-28). Data as JSON: /api/errors/7ca8d0a7a843a095. Report an issue: GitHub.